#include <iostream>
using namespace std;
int main() {
  int n;
  int a[200000+1];
  int i;

  cin >> n;
  for (i=0; i<n; i++) cin >> a[i];

  int min = 300000000+1;
  int x;
  for (i=0; i<n-2; i++) {
    if (((a[i] < a[i+1]) && (a[i+1] > a[i+2])) ||
        ((a[i] > a[i+1]) && (a[i+1] < a[i+2]))) {
      x = a[i]+a[i+1]+a[i+2];
      if (x < min) min = x;
    }
  }
  if (min == 300000000+1) min = -1;
  cout << min;
  return 0;
}